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Poplar-loosestrife aphidsOn this page: Mordwilkoja vagabunda
Mordwilkoja has undeveloped antennal tubercles. Antennal segment II is about 1.4 times longer than segment I (cf. Pemphigus, which has segment II approximately the same length as segment I). Secondary rhinaria are annular. The antennal terminal process is longer than the base of antennal segment VI in the spring migrant, and 2-3 times the base in sexuparae. The terminal process in the spring migrant has characteristic clear spots of unknown function. The apical rostral segment is 3 times as long as its width at base. The forewing media vein is unbranched, and the hindwing has two cross veins with the bases joined or nearly joined. The siphunculi are absent or obscure, and the cauda is round.
There is only species of Mordwilkoja, which lives in North America. It galls its primary host, poplar (Populus) and host alternates to loosestrife (Lysimachia). Blackman in Aphids on Worlds Plants. notes that its secondary host generations are very similar to those of some Thecabius species (subgenus Parathecabius).
Mordwilkoja vagabunda (Poplar vagabond aphid) USA, Canada, Germany?, Japan?
Galls caused by Mordwilkoja vagabunda are large, irregular, bladder-like growths formed from stipules at the bases of terminal twigs of cottonwood poplars. Young galls are green, but as they mature they develop small, red, blister-like elevations on the peripheral ridges (see first picture below). These later become necrotic and form openings into the gall interior. These holes, whose development coincides closely with the development of alate aphids, allow these migrants to escape the galls. Old galls turn black, and as such are very conspicuous.
The first-instar fundatrix of Mordwilkoja vagabunda feeds on the ventral surface of a stipule, causing the tip and margins to grow outwards from the stem, thus creating the gall. The fundatrix in the gall has 4-5 segmented antennae, and wax plates on the thorax and abdomen. The offspring of the fundatrix (= fundatrigeniae) are yellow-gray and thickly wax-covered, and develop to emigrant alatae which fly to a secondary host. The fourth instar fundatrigeniae (see second picture below) have wing pads the same color as the thorax, but dark at the base.
First image William M. Ciesla, Bugwood.org under a creative common licence,
The alate emigrant (see third picture above) has the head and thorax brown, and the abdomen green. Their appendages are dusky. The antennae are 6-segmented, with 8-12 elliptical secondary rhinaria on antennal segment III, and 1-3 on segment IV. The terminal process is distinctly longer than the base of antennal segment VI, and bears 2-3 clear spots of unknown function, each with a small dagger-like stipule. The rostrum reaches to between the first and second pairs of coxae. The media vein of the fore wing is simple. The siphunculi are hardly more than mere rings which are often difficult to observe. Wax glands are distributed one pair on each of the prothorax & mesothorax, and two pairs, lateral and dorsal, on each abdominal segment. The cauda and anal plate are rounded. The body length of the alate Mordwilkoja vagabunda emigrant is 1.8-2.4 mm.
Mordwilkoja vagabunda apterae on the secondary host, Lysimachia have 6-segmented antennae. Antennal segment III is as long as, or longer than, segments IV+V together (cf. Thecabius lysimachiae & Thecabius auriculae on Lysimachia which, if antennae are 6-segmented, have segment III distinctly shorter than segments IV+V together). There are wax plates on the abdomen. Siphunculi are absent. Alate sexuparae differ from the emigrant alatae by having the terminal process shorter than the base of antennal segment VI, and by lacking siphunculi.
Mordwilkoja vagabunda host alternates between cottonwood (mainly Populus deltoides) and creeping jenny (Lysimachia spp.). On the primary host they induce large, irregular, multi-lobed galls, formed from the leaf stipules. Emigrant alatae emerge from galls in May-June and found colonies on stems, leaves or roots of creeping jenny (Lysimachia). Mordwilkoja vagabunda is found as a host alternating species in USA and Canada but, what appear to be anholocyclic secondary host generations, have also been found on Lysimachia roots in Germany and Japan.